Many modern communications systems use channel state information reference signals (CSI-RS) transmitted by an Evolved NodeB (eNB) to assist User Equipment (UE) in measuring communications channels between the eNB and the UE. As an illustrative example, the eNB transmits a CSI-RS and a UE uses it to measure the communications channel and generate channel information, such as a channel quality indicator (CQI), precoding matrix index (PMI), rank indicator (RI), and the like, which it feedbacks to the eNB. eNBs may also commonly be referred to as NodeBs, base stations, access points, base terminal stations or transmission points, and the like, while UE may also be commonly referred to as mobile stations, mobiles, terminals, users, subscribers, and the like.
Generally for Massive Multiple Input Multiple Output (massive MIMO) or 3D MIMO communications systems, there are large numbers of transmit antennas (or ports) at the eNB. Therefore, the eNB would have to transmit a large number of CSI-RS signals in order to facilitate channel information between each transmit antenna (or ports) and each receiver antenna at each UEs. The transmission of the large number of CSI-RS would significantly impact overall communications system performance by consuming a large amount of network resources as overhead.